Heat lights have therapeutic applications when applied to human skin. Some heat lights make use of liquid heat filters to reduce the user's exposure to light with harmful characteristics.
Liquid-containing heat filters for high-intensity lights experience severe changes in temperature due to the intensity of the light they filter. Such a severe change in temperature causes an unacceptable and even dangerous expansion of the housing of the filter, due to the heating and expansion of the liquid. This is particularly important in the event that the liquid-containing heat filter is used on a high-intensity light for health related purposes.